NASA's Next Rocket May Shake Too Much

By
Seth Borenstein, AP Science Writer
|
January 18, 2008 09:05pm ET

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An artist's rendition of Ares I being stacked in the vehicle assembly building at NASA's Kennedy Space Center in Florida. Houston-based Boeing won NASA's contract to built the rocket's upper stage, which appears in orange below the conical Orion crew capsule.

Credit: NASA.

WASHINGTON (AP) - NASA is
wrestling with a potentially dangerous problem in a spacecraft, this time in a
moon rocket that hasn't even been built yet.

Engineers are concerned
that the new rocket meant to replace the space shuttle and send astronauts on their
way to the moon could shake violently during the first few minutes of
flight, possibly destroying the entire vehicle.

?They know it's a real
problem,'' said Carnegie Mellon University engineering professor Paul
Fischbeck, who has consulted on risk issues with NASA in the past. ?This thing
is going to shake apart the whole structure, and they've got to solve it.''

If not corrected, the
shaking would arise from the powerful first stage of the
Ares I rocket, which will lift the Orion crew capsule into orbit.

NASA officials hope to have
a plan for fixing the design as early as March, and they do not expect it to
delay the goal of returning astronauts to the moon by 2020.

?I hope no one was so
ill-informed as to believe that we would be able to develop a system to replace
the shuttle without facing any challenges in doing so,'' NASA administrator
Michael Griffin said in a statement to The Associated Press. ?NASA has
an excellent track record of resolving technical challenges. We're confident
we'll solve this one as well.''

Professor Jorge Arenas of
the Institute of Acoustics in Valdivia, Chile, acknowledged that the problem
was serious but said: ?NASA has developed one of the safest and risk-
controlled space programs in engineering history.''

The space agency has been
working on a plan to return to the moon, at a cost of more than $100 billion,
since 2005. It involves two different rockets: Ares I, which would carry the
astronauts into space, and an unmanned heavy-lift cargo ship, Ares V.

The concern isn't the
shaking on the first stage, but how it affects everything that sits on top: the
Orion crew capsule, instrument unit, and a booster.

That first stage is
comprised of a five-segment reusable solid rocket booster derived from the type that
NASA uses to launch the shuttle and would be built by ATK Launch Systems of
Brigham City, Utah.

The shaking problem, which
is common to solid rocket boosters, involves pulses of added acceleration
caused by gas vortices in the rocket similar to the wake that develops behind a
fast-moving boat, said Arenas, who has researched vibration and space-launch
issues.

Those vortices happen to
match the natural vibrating frequencies of the motor's combustion chamber, and
the combination causes the shaking.

Senior managers were told
of the findings last fall, but NASA did not talk about them publicly until the
AP filed a Freedom of Information Act request earlier this month and the
watchdog Web site Nasawatch.com submitted detailed engineering-oriented
questions.

The response to those
questions, given to both Nasawatch and AP, were shared with outside experts,
who judged it a serious problem.

NASA engineers
characterized the shaking as being in what the agency considers the ``red
zone'' of risk, ranking a five on a 1-to-5 scale of severity.

?It's highly likely to
happen and if it does, it's a disaster,'' said Fischbeck, an expert in
engineering risks.

The first launch of
astronauts aboard Ares I and Orion is set for March 2015.